Rössler N, Klein R, Scholz H, Witte A
Institute of Microbiology and Genetics, University of Vienna, Dr Bohr-Gasse 9, A-1030 Vienna, Austria.
Mol Microbiol. 2004 Apr;52(2):413-26. doi: 10.1111/j.1365-2958.2003.03983.x.
The sequence of phi Ch1 contains an open reading frame (int1) in the central part of its genome that belongs to the lambda integrase family of site-specific recombinases. Sequence similarities to known integrases include the highly conserved tetrad R-H-R-Y. The flanking sequences of int1 contain several direct repeats of 30 bp in length (IR-L and IR-R), which are orientated in an inverted direction. Here, we show that a recombination active region exists in the genome of phi Ch1: the number of those repeats, non-homologous regions within the repeat clusters IR-L and IR-R and the orientation of the int1 gene vary in a given virus population. Within this study, we identified circular intermediates, composed of the int1 gene and the inwards orientated repeat regions IR-L and IR-R, which could be involved in the recombination process itself. IR-L and IR-R are embedded within ORF34 and ORF36 respectively. As a consequence of the inversion within this region of phi Ch1, the C-terminal parts of the proteins encoded by ORF34 and 36 are exchanged. Both proteins, expressed in Escherichia coli, interact with specific antisera against whole virus particles, indicating that they could be parts of phi Ch1 virions. Expression of the protein(s) in Natrialba magadii could be detected 98 h after inoculation, which is similar to other structural proteins of phi Ch1. Taken together, the data show that the genome of phi Ch1 contains an invertible region that codes for a recombinase and structural proteins. Inversion of this segment results in a variation of these structural proteins.
phi Ch1的序列在其基因组中部包含一个开放阅读框（int1），该开放阅读框属于位点特异性重组酶的λ整合酶家族。与已知整合酶的序列相似性包括高度保守的四联体R-H-R-Y。int1的侧翼序列包含几个长度为30 bp的直接重复序列（IR-L和IR-R），它们呈反向排列。在此，我们表明phi Ch1的基因组中存在一个重组活性区域：在给定的病毒群体中，这些重复序列的数量、重复簇IR-L和IR-R内的非同源区域以及int1基因的方向各不相同。在本研究中，我们鉴定出由int1基因以及向内定向的重复区域IR-L和IR-R组成的环状中间体，它们可能参与重组过程本身。IR-L和IR-R分别嵌入在ORF34和ORF36内。由于phi Ch1该区域内的倒位，由ORF34和36编码的蛋白质的C末端部分发生了交换。在大肠杆菌中表达的这两种蛋白质都与针对整个病毒颗粒的特异性抗血清相互作用，表明它们可能是phi Ch1病毒粒子的组成部分。在接种98小时后，可以检测到嗜盐碱红菌中该蛋白质的表达，这与phi Ch1的其他结构蛋白相似。综上所述，数据表明phi Ch1的基因组包含一个可倒位区域，该区域编码一种重组酶和结构蛋白。该片段的倒位导致这些结构蛋白发生变异。
